Vibrational spectra and analysis on the molecule of
potassium pentaborate crystal (KB5)

V Joseph*, V Santhanam#,
S Gunasekaran†, P Sagayaraj* & S Ponnusamy‡

*Department of
Physics, Loyola College, Chennai 600 034

Received 15 May 2002;
revised 28 August 2002; accepted 26 November 2002

Potassium pentaborate
(KB5) crystals have been grown by solution growth technique. A structural
investigation on the KB5 crystal is made, using FTIR and laser Raman spectra.
The molecular structure of KB5 belongs to C2V symmetry considering the hydroxyl
group as point mass. The total number of normal modes of vibration is 39 and are
distributed as Gvib = 14A1 + 5A2 + 10B1 + 10B2. A normal coordinate analysis has
been carried out with an orthonormal set of symmetry coordinates following
Wilson F-G matrix method. The potential constants evaluated for this molecule
are found to be in good agreement with literature, thereby, confirming the
vibrational assignments. To check whether the chosen set of vibrational
frequencies contributes maximum to the potential energy associated with the
normal coordinates of the molecule, the potential energy distribution has been
evaluated. Further, the thermogravimetric analysis (TGA) confirms the
decomposition of KB5 taking place in two stages. The differential scanning
calorimetry (DSC) curve of KB5 crystals has been recorded in the temperature
range 50-580 °C. The phase transition temperature and enthalpies of KB5 were
measured and the results are discussed.

Numerical solution of hydromagnetic unsteady

free convection flow past an infinite porous plate

Atul Kumar Singh

Department of
Mathematics, VSSD College, Kanpur 208 002

Received 1 March 2002;
revised 12 November 2002; accepted 28 December 2002

Unsteady free
convection flow of an incompressible, electrically conducting, viscous fluid
past an infinite vertical porous flat-plate under the influence of uniform
magnetic field, applied normal to the flow, has been studied by finite
difference method. The uniform suction is considered normal to the plate. The
results for the velocity distribution, the temperature distribution and the
skin-friction have been investigated and discussed for different values of the
parameters encountered in the equations.

variation in Bi content

*Department of
Electronic Science, University of Delhi, South Campus, New Delhi 110 021

Received 12 July 2002;
revised 24 October 2002; accepted 27 January 2003

Alloys of Te-Bi-Se
glass system, obtained by rapid quenching technique, have been characterized by
calorimetric measurements and differential thermal analysis for different
heating rates. Variation in two important parameters, namely, glass transition
temperature Tg and glass forming ability Kgl have been studied with variation in
Bi content at various heating rates. By analyzing the results, it has been seen
that, with the increase in Bi content, the glass forming ability Kgl decreases.
However, with the increase in heating rates, the glass transition temperature Tg
is found to increase. This analysis helps in finding the suitability of an alloy
to be used in phase transition optical memories/switches. The results have been
analyzed using Kissinger’s equation for non-isothermal crystallization of
materials.

Field-emission in diamond-like carbon films grown by

various techniques

Received 22 August
2002; revised 30 October 2002; accepted 1 January 2003

The field-emission
measurements from ~0.5 µm thick hydrogenated amorphous carbon (diamond-like
carbon) films grown by a variety of easily implementable plasma enhanced
chemical vapour deposition (PECVD) based techniques and also by a method that
uses a saddle-field fast atom beam source, have been reported. Field-emission
behaviour in these materials has been discussed in the light of residual stress,
hardness, optical bandgap, and characteristic energy of band tails (Urbach
energy). Onset emission fields as low as~ 6V/µm, together with low residual
stress of 0.25 GPa, hardness of 17.5 GPa, optical bandgap of 1.5 eV and Urbach
energy of 165 meV, have been obtained in diamond-like carbon films grown by
pulsed-PECVD at 13.56 MHz. DLC films of comparable quality could also be grown
using a saddle-field fast atom beam source, which operates on modest dc power
supply and with no heated filaments or magnets.

Acoustics and thermodynamics of alcoholic solution of

calcium nitrate

Received 21 March
2002; revised 6 August 2002, accepted 2 January 2003

Apparent partial
molal volumes and compressibilities of calcium nitrate in six alcohols
have been determined at 296.15 K from precise density and ultrasound velocity
measurements. They have been related with each other, as well as with free
energy of the solutions.

after high-energy heavy ion irradiation

Crystallization
kinetics of virgin and irradiated (at three different fluences with high energy
heavy ion; Ni11+ of (150 MeV) specimens of Fe78B13Si9 glass has been studied
using Differential Scanning Calorimetry (DSC) under non-isothermal condition.
Only one set of geometry has been used for irradiation at different fluences. It
has been found that, the crystallization process is completed in two phases. The
DSC data have been analyzed in terms of kinetic parameters, viz. activation
energy (Ec), Avrami exponent (n), dimensionality of growth (m) and frequency
factor (Ko) using two different theoretical models. The lower activation energy
in case of second crystallization occurring at higher temperature indicates the
easier nucleation of second phase, which is termed Fe2B bct phase. The
abnormally high value of Avrami exponent indicates very high nucleation rate
during second crystallization.

Fluorescence properties of Nd3+ doped B2O3-P2O5-Li2SO4
glass

V Aruna, N Sooraj
Hussain & N V V Prasad

Department of
Physics, Sri Venkateswara University, Tirupati 517 502

Received 2 September
2002; accepted 6 January 2003

The production of
neodymium glass in the chemical composition of 44.75 B2O3-44.75P2O5-10Li2SO4 has
been reported. An intense up-converted violet colour emission has been observed
upon excitation with a yellow light. The violet colour up-conversion process has
been explained by an energy level scheme. By correlating the measured
fluorescence life-time results with the absorption data, the quantum efficiency
(h=44%) of the optical material has been evaluated from the application of Judd-Ofelt
theory.

Received 17 June 2002;
revised 13 January 2003; accepted 27 January 2003

The II-VI materials
of Zn1-xMxO have been synthesized by solid-state reaction method and their
structural, electrical and dielectric properties studied. The lattice parameters
of these materials are found to be consistent with the reported values. The
dielectric constant measured at different five frequencies agrees well with the
published values and found to be maximum for doping concentration x = 0.2, at
all frequencies. A dc resistive anomaly was found for all samples at a certain
temperature called transition temperature (Td-s) from dielectric to
semiconducting state, which depends on the concentration and nature of the
dopant atoms in ZnO.

Non-linear cross-talk analysis in fiber Raman amplifiers

Received 5 June 2002;
revised 20 September 2002; accepted 22 January 2003

Optical non-linearities
limit the optical power and information capacity of light-wave systems. These
non-linearities introduce different types of frequency and phase distortions,
which lead to cross-talk. Various non-linear effects that affect Raman
amplification have been discussed and an evaluation of the cross-talk induced
due to these effects, has been presented. The maximum input power that can
be transmitted in a WDM system without degrading its performance has also been
evaluated.

A new analytical
model for tri-step doped InAlAs/InGaAs heterostructure InP based HEMT has been
proposed in this paper. Maximum sheet carrier density has been formulated
considering the limitation arising from the doping-thickness product. A
comparison is made between conventional pulsed doped structure and equivalent
tri-step doped structures to validate the model. The conventional pulsed doped
device is also optimized for higher sheet carrier concentration/effective
parallel conduction voltage/transconductance/cut-off frequency by varying the
Schottky layer thickness for identical carriers using equivalent tri–step doped
structure.

X-ray, K-absorption near edge structural study of some

copper(II) complexes with amino acids as ligands

Received 29 May 2002,
revised 18 December 2002, accepted 28 January 2003

X-ray, K-absorption
spectra of five copper (II) complexes have been recorded using a 0.04 m radius
Cauchois type, curved crystal spectrograph. Parameters like, chemical shift,
edge width, effective nuclear charge, percentage covalency, shift in principal
absorption maxima etc. have been calculated and used to interpret the structural
details of the complexes. Wiener indices have also been calculated for the
complexes.

The satellite spectra
arising due to L3Mx-MxN4,5 (x ş 1-5) transition array in X-ray emission spectra
of 75Re, 77Ir and 79Au, have been calculated, using available Hartree–Fock–Slater
(HFS) data on K-LM and L-MN Auger transition energies. The agreement between the
calculated and measured energies, between calculated and measured separations in
energies and the consideration of the relative probabilities of all the
L3Mx-MxN4,5 transitions have been used as the basis for deciding the origin of
the satellites. It has been established that, two satellites observed in the Lb2
region of the X-ray spectra of the elements with Z=75 to 79, named b2I and b2II
in order of increasing energy are mainly emitted by L3M4,5-M4,5N4,5 transitions.
The satellite b2I has been assigned to the super-position of the transitions
3F4-3G5 and 3F4-3D3, contributing in order of decreasing intensity, and the line
b2II, has been assigned to mainly the 1F3-1G4 and 3P0-3D1 transitions. The
possible contributions of other transitions of the L3Mx-MxN4,5 (x ş 1-5) array
having appreciable intensities have also been discussed.

NEWS SCAN

Emerging technology of quantum dot lasers

Laser light is very
different from normal light. It is monochromatic, coherent, directional, very
strong and concentrated. Lasers emit radiation at a single wavelength.
Therefore, the applications which require many wavelengths need several lasers.
Quantum wells can be engineered to emit different wavelengths. A quantum well is
a layer of semiconducting material embedded in a semiconductor with a larger
bandgap. The charge carriers - the electrons can then be trapped in a well where
these can occupy certain quantised energy states, similar to the electrons in an
atom. Semiconductor lasers play a major role in many technological products like
compact disk players, optical data storage, a bar code readers , laser printers
and optical communication.(C Gmachi et al.,415,Nature,883).